This invention relates to vaccines useful, for example, for modulating immune responses in subjects to a variety of antigens.
The innate immune system comprises those mechanisms that have evolved over millennia to provide first line defense against foreign antigens and an antigen recognition repertoire which does not diversify during the ontogeny of the individual. This is in contrast with the acquired immune system which provides later phase defense mechanisms and depends on a repertoire of antigen-specific molecules, e.g., immunoglobulins and T cell receptors that diversify over the ontogeny of the individual. Innate immune mechanisms can contribute to initiation of an antigen-specific response by the acquired immune system, for example by facilitating uptake of antigen by antigen-presenting cells (APCs), which can thereafter stimulate cognate T cells.
Opsonins of the innate immune system (xe2x80x9cinnate opsoninsxe2x80x9d) are known in the art as secreted polypeptide molecules of the innate immune system and can remain bound to an antigen and to the surface of an APC at the same time. They can thus act as xe2x80x9cbridgesxe2x80x9d, and are thought, by virtue of this property, to promote internalization of antigens by APCs. The mode in which opsonins bind to antigens varies among opsonins, and can be covalent or noncovalent. In general, the antigen-binding moieties of innate opsonins differ from the antigen-binding moieties of immunoglobulins in that the former are relatively invariant among members of the same species, and do not undergo diversification during the ontogeny of an individual.
There have been a number of attempts to increase uptake of antigens by APCs by coupling an antigen via a non-peptide linkage to another molecule that can bind to the surface of an APC. Targeting moieties have included, for example, C3b (Jacquier-Sarlin et al., Immunol 84:164-70; Arvieux et al., Immunol 65:229-35), alpha-2 macroglobulin (Chu et al, J Immunol 152:1538-45; Chu and Pizzo, J. Immunol 150:48-58), and molecules comprising idiotypes specific for immunoglobulin Fc receptors (Squire et al., J Immunol 152:4388-96; Gosselin et al., J Immunol 149:3477-81; Snider and Segal, J Immunol 143:59-65) or class II MHC molecules (Estrada et al., Vaccine 13:901-7; Berg et al., Eur J Immunol 24:1262-8; Carayanniotis and Barber, Nature 327:59-61).
Another approach to improving uptake of antigen by APCs has been to construct chimeric polypeptides comprising an antigen and an idiotypic portion of an antibody, in which the latter is specific for class II MHC molecules (Baier et al., J Virol 69:2357-65) or an immunoglobulin Fc receptor (Liu et al., JCI 98:2001-7).
Dempsey et al. (Science 271:348-50) constructed fusion proteins between C3d and an antigen, the fusion proteins being capable of binding to CR2-bearing cells such as B cells, reasoning that the B cell costimulation provided by C3d would increase the humoral immune response to the antigen. Marked increases in antibody response were in fact observed, which were abrogated by in vivo antibody blockade of CR2.
The invention provides compositions and methods for modulating immune responses in subjects. The invention is based, at least in part, on the discovery that an in-frame translation fusion of an antigen with an APC binding domain of an opsonin forms a molecule, that is, a fusion polypeptide, which when administered to a subject modulates an immune response to the antigen.
Accordingly, the invention also pertains to recombinant nucleic acid molecules which include a nucleotide sequence encoding an antigen and a nucleotide sequence encoding an APC binding domain, and thus include a nucleotide sequence encoding a fusion polypeptide comprising the antigen and the APC binding domain.
As used herein, xe2x80x9cmodulationxe2x80x9d means that a desired/selected response is more efficient, more rapid, greater in magnitude, and/or more easily induced than if the antigen had been used alone. The desired immune response can be stimulation/activation of a selected immune response, e.g., selective enhancement of an immune response to an antigen, or it can be inhibition of a selected immune response e.g., selective suppression, elimination, or attenuation of an immune response to an antigen, or a combination thereof.
As used herein, an xe2x80x9cAPC binding domainxe2x80x9d refers to the whole of an innate opsonin or that portion or domain of an innate opsonin that binds to antigen presenting cells (APC binding domain).
In a fusion polypeptide according to the invention, different peptides or polypeptides are linked in-frame to each other to form a contiguous chimeric polypeptide. Thus, a first portion of the fusion polypeptide comprises an antigen and a second portion of the fusion polypeptide, either the amino- or carboxy-terminal to the first portion, comprises a function opsonin moiety. It is critical in the fusion polypeptide that the antigen retain its antigenicity and the APC binding domain retains its ability to facilitate or permit binding of the fusion polypeptide to the APC; that is, the two portions of the fusion polypeptide must be able to assume their natural structure to the extent that they retain the antigenicity and binding functions necessary to modulate the immune response according to the invention. The amino and carboxy-terminal orientation of the antigen and APC binding domain will most likely be determined by the location of the APC binding domain in the opsonin molecule; that is, if the APC binding domain is located near the amino terminus of the opsonin, then the amino-terminal portion of the opsonin may correspond to the amino terminus of the fusion polypeptide; similarly, if the APC binding domain is located near the carboxy terminus of the opsonin, then the amino-terminal portion of the opsonin may correspond to the carboxy terminus of the fusion polypeptide.
Examples of categories of antigens which can be encoded by the nucleic acid molecules include, for example, viral antigens, bacterial antigens, fungal antigens, protozoal and other parasitic antigens, tumor antigens, antigens involved in autoimmune disease, allergy and graft rejection, and other miscellaneous antigens.
APC binding domains of innate opsonins encoded by the nucleic acid molecules can include, for example, an APC binding domain of fibronectin, xcex12macroglobulin (a2m), C-reactive protein (CRP), complement component C1q, complement fragment C3b, complement component C4b, mannose binding protein, conglutinin, and surfactant proteins A and D.
The nucleic acid molecules of the invention can be used, for example, to modulate an immune response in a mammal to an antigen encoded by the nucleic acid molecule by direct administration of the nucleic acid.
Methods of the invention include the step of administering to an animal a nucleic acid molecule which encodes a fusion polypeptide comprising an antigen and a APC binding domain of an innate opsonin, or which encodes a polypeptide complex as defined herein, in an amount and over a period of time effective to modulate an immune response to the antigen in the mammal.
As used herein, an xe2x80x9canimalxe2x80x9d refers to a non-rodent animal, preferably, a non-rodent mammal, more preferably, a primate, and most preferably, a human.
The invention also pertains to vectors which include the nucleic acid molecules of the invention, host cells which are transfected with such vectors, and transgenic animals which include the nucleic acid molecules of the invention.
In another embodiment of the invention, where a first and second portion of an opsonin, when covalently associated via a non-peptide bond, form an APC binding domain, the first or second portion of the opsonin may be fused in-frame to the antigen to form a fusion polypeptide. The remaining second or first portion, respectively, may then be covalently associated with the fusion polypeptide via a natural mechanism in the host cell and form a complex.
Therefore, in another aspect, the invention pertains to a multichain polypeptide complex comprising a first portion of an innate opsonin which in the presence of a second portion of an innate opsonin forms an APC binding domain, and a fusion polypeptide that comprises an antigen and the second portion of the opsonin. The first portion of the innate opsonin is associated with the fusion polypeptide containing the second portion of the opsonin via a covalent linkage. Therefore, the polypeptide complex comprises at least two polypeptide chains which, when covalently associated, form an APC binding domain. Furthermore, at least one of the chains may comprise an antigen.
Antigens and opsonins which can provide components of the fusion polypeptides are described herein.
In yet another aspect, the invention pertains to vaccine compositions. The vaccine compositions include nucleic acid molecules including nucleotide sequences encoding a fusion polypeptide or a polypeptide complex as described herein and a pharmaceutically acceptable carrier.
The vaccine compositions of the invention can be used for, for example, modulating in an animal an immune response to the antigen.
Methods of administering a vaccine according to the invention include the step of administering naked nucleic acid, which may be RNA or DNA, to the animal. As used herein, xe2x80x9cnakedxe2x80x9d refers to nucleic acid which is substantially free from substances which facilitate entry of the nucleic acid into a host cell, for example, liposomes, ligands specific for cell surface receptors, endosomal disruption agents, etc.